Crops Keeping Chicago Cooler?

The following information is a Web Extra from the pages of Farm Journal. It corresponds with the article "Mercury Rising." You can find the article in Farm Journal's October 2012 issue.

With a few exceptions, Chicagoans have been enjoying relatively milder summers in recent years. According to one researcher, they may want to thank area farmers.

David Changnon, a climate scientist at Northern Illinois University, has spent more than a decade studying how evapotranspiration (ET) might be affecting weather regionally across the Midwest.

Ever get a chill in the wintertime stepping out of the shower? That’s ET at work – the rapid evaporation is removing heat from your body, Changnon says. In the real world, more water vapor in the lower atmosphere means higher dew points and lower chances for extremely hot summer days.

ET also means that a well-watered, vigorous corn and soybean crop can act as a natural air conditioner. His working hypothesis is that changes in farming that have led to more densely populated, higher yielding corn and soybeans have also lead to "excessive ET" that helps regulate summertime temperatures across the Midwest.

"The crop can act as a thermostat for the lower atmosphere," he says. "Added water vapor kind of puts a cap on how hot it could get during the summer."

Critics of this theory might point to record-breaking heat across the Midwest, but Changnon says this anomaly actually reinforces his research. Because the region experienced a mostly drier, hotter spring, the crops lacked the "fuel" they needed to pump out water vapor en masse as they normally would.